This invention relates to improved apparatus for coupling microwave energy from a coaxial transmission line to a rectangular waveguide and vice versa.
Various coaxial-to-waveguide transitions are known in the prior art. The function of such transitions is to couple microwave energy from the coaxial line to the waveguide and vice versa, but it is desired to accomplish this function in a manner that minimizes the reflected microwave energy resulting from the transition. In other words, an impedance transformer is required at the coaxial to waveguide transition to minimize the standing wave ratio and reflected energy or return loss in the transmission line. Moreover, it is desirable that this minimization be effective over a wide frequency band. The "conventional" coaxial-to-waveguide transition comprises a waveguide having a closed end and a coaxial line connection mounted in one of the wide walls of the waveguide so that the coaxial line center conductor enters the waveguide in its E-plane. Coaxial lines that enter the waveguide from one of its ends also are known. The center conductor contacts one of a series of progressively larger blocks mounted in the waveguide as an impedance transformer. The conventional and other transitions are described or illustrated in the following publications: Gershon J. Wheeler, "Broadband Waveguide-to-Coax Transitions," IRE National Convention Record (Part 1), pp. 182-185, Mar. 18-21, 1957; Chao Chun Chen et als, "Ultra-Wideband Phased Arrays," Hughes Aircraft Company Contract Report to the Air Force Cambridge Research Laboratories, AFCRL-TR-73-0569, pp. 2-18 to 2-24, July, 1973; and J. C. Dix, "Design of Waveguide/Coaxial Transition for the Band 2.5-4.1 GHz," Proceedings of the IEEE, Vol. 110, pp. 253-255, February 1963.